There is known a hoisting machine comprising a vertical pole having a guide along which carrying elements move. Provided at the carrying element closest to the top of the pole is a bracket for attaching a weight thereto. The carrying elements are moved along the guide by a hydraulic cylinder positioned at the bottom of the pole. The carrying elements are brought close to the pole and removed therefrom manually (cf., SE, C, 417,082).
However, manual displacement of the carrying elements makes the machine less reliable in operation and complicates its servicing.
There is also known a hoisting machine comprising a tubular pole having weight and build-up branches extending in parallel along the pole and having carrying elements movable along the branches, a bracket for securing the weight bearing on the carrying element closest to the top of the pole, and a mechanism for moving the carrying elements along the branches and displacing them from one branch to the other positioned at the base of the pole.
This mechanism includes a vertical hydraulic cylinder having two rods and positioned so that the rods are coaxial with the build-up and weight branches, accordingly, and a horizontal hydraulic cylinder whose rod has a clamp means for gripping the carrying element to displace it from under one branch to the other branch, and further having spring-loaded pivotable stops under each branch provided with lugs for restricting, in the drawn-together position of the stops, the movement of the carrying elements under the force of gravity, and a removable sleeve fitted onto the first or second rod of the vertical hydraulic cylinder depending on the direction of movement.
Operation of this hoisting machine meets with difficulties associated with ensuring strictly alternate functioning of the vertical and horizontal hydraulic cylinders, which makes the machine less reliable. In addition, in order to draw the pivotable stops under the weight branch apart, the removable sleeve positioned at the rod of the vertical hydraulic cylinder coaxially with the weight branch takes up loads both vertically from the weight and carrying elements present, in the weight branch and horizontally as a result of friction between the lugs of the pivotable stops and end face of the carrying element proportional to the mass of the weight, which necessitates an extra force to be applied by the vertical hydraulic cylinder and results in excessive wear of the pivotable stops and surface of the removable sleeve.
There is further known a hoisting machine comprising a tubular pole with weight and build-up branches extending in parallel along the pole and having carrying elements capable of movement along the branches, a bracket for securing the weight to be lifted bearing on the carrying element closest to the top of the pole in the weight branch, a mechanism for moving the carrying elements lengthwise of the branches and displacing them from one branch to the other positioned at the base of the pole and having a housing accommodating a hydraulic cylinder positioned so that the axis of its rod runs in line with the axis of the weight branch, the rod having two pins coaxial with the respective branch, and a frame with rollers capable of travelling in a plane perpendicular to its axis in a direction from one pin to the other, whereby the frame can assume two extreme positions determining elevation or lowering of the weight, pivotable stops under each branch having lugs for restricting, in the drawn-together position of the stops, the movement of the carrying elements under the action of the force of gravity, and shaped surfaces intended to engage with the frame rollers, whereby as the rod of the hydraulic cylinder moves to the base of the branches the stops are drawn apart to disengage from the carrying elements, the spring mechanism for returning the stops to the drawn-together position, the guide means connected to the stops and determining the travel path of the carrying elements from one branch to the other, two-pushers capable of movement toward each other in a plane perpendicular to the axis of the cylinder rod and engagement with the side surface of the carrying element present in the guide means for transferring it from one branch to the other alternately kinematically linked each by way of a two-arm lever whose axis of oscillation is secured to the housing of the mechanism with the corresponding side of the frame in one of its extreme positions determining the direction of movement of the carrying elements in the branches of the pole.
This prior art hoisting mechanism further includes pairs of springs connected to each stop, one such spring being connected by a first end thereof to the housing of the mechanism, and by the other to the pivotable stop, the second spring being connected by the first end thereof to the piovotable stop and by the second end to the shaped surface which is part of a four-link chain defined by the pivotable stop, shaped surface, connection of the shaped surface to the pivotable stop, and connection of the spring end secured at the pivotable stop to the shaped surface (cf., SU, A, 1,051,025).
However, one disadvantage of this known machine is that it can operate only in the vertical position of the pole. For example, it is impossible to use the aforedescribed construction of the mechanism for moving the carrying elements in an inclined position, such as for pivoting the pole with a weight to be lifted to the vertical position. With the pole in an inclined position the pivotable stops are acted upon by a moment of force determined by a component force of the pull of gravity of the pivotable stops to result in bringing the stops inadvertently apart and consequently in opening of the guide means connected to the stops, and in the carrying element tending to get out of the guide means rendering the machine inoperable.
Therefore, the known hoisting machine necessitates accurate selection and adjustment of the springs of the spring mechanism for returning the pivotable stops to the drawn-together position ensuring that the carrying elements are reliably fixed in place, the pivotable stops are brought together and spread apart at the precise point of passing of the carrying elements whereas with the pole in an inclined position the equilibrium in the springs of the return mechanism can be disturbed to affect the reliability of the hoisting machine.